DigitalOcean

Unlike Heroku, you will need to manually configure your server and setup the deployment process.

There is one-click setup for some common cases, like Rails, that gets the environment ready.
Deploys are still up to you, though.

Nominal DO cost is cheaper — $5 for what would be $7+ on Heroku, but you also have to take opportunity cost into account.
It takes time and effort to set everything up.
For small to medium apps, Heroku is clearly a better option, but once you outgrow it, DO looks like a great alternative.